The invention concerns a combustion chamber for reciprocating-piston internal combustion engines as set forth in the classifying portion of claim 1.
The requirements made in respect of reciprocating-piston internal combustion engines are a low level of pollutant emission and a low specified fuel consumption, that is to say, little fuel is to be burnt. The following conditions must be observed in order to satisfy those requirements: a high level of fresh gas acceleration, a high fresh gas speed, turbulence-free flow, a deflector surface on the piston crown, a guide element for fresh gases, a combustion chamber in the cylinder head and in the piston crown, concentration of the fresh gases in the center of the combustion chamber, a high degree of compression, and rapid combustion.
German patent specification No. 32 24 337 describes a piston with a spherical squish gap and a combustion chamber which is partially formed in the piston crown. The spherical configuration of the piston crown is to accelerate the potential flow of the fresh gases in the compression stroke, while at the same time there is a rotational flow circulating in the same direction in the direction of the cylinder axis, but in the opposite direction in relation thereof. At the top dead center point the potential flow is urged into the combustion chamber by the spherical squish surface. When that happens the particles of fuel which are disposed in the outer edge region of the potential flow are also conveyed inwardly. A rich mixture is formed in the combustion chamber at the edge of the rotational flow, and is fired by two spark electrodes. Due to the piston crown being advantageous in terms of flow configuration, the fuel particles of the potential flow are in the region of the cylinder wall and at top dead center are conveyed into the upper part of the combustion chamber by the pressure occurring in the squish surfaces. The rotational flow prevents penetration into the center of the combustion chamber. That also explains the arrangement of two spark electrodes.
The same considerations apply to British patent specification No. 1 119 298 as apply to German patent specification No. 32 24 337 as the combustion chamber, the piston crown, and the squish surfaces have the same features. In this case, at top dead center, the fresh gases are urged by way of passages to the spark electrode, and fired. The flame flashes back by way of the passages into the combustion chamber and ignites the remaining fresh gases. As the passages act as throttle means, this arrangement must be expected to involve losses in terms of pressure and power. In addition, there is a delay in regard to combustion of the whole of the fresh gases, which results in an increase in the harmful hydrocarbons in the exhaust gas.
In German patent specification No. 37 18 083 the piston crown, which is in the form of a ridge or saddle roof, does not permit an uninterrupted flow of the fresh gases. Eddy flows occur at the mutually oppositely disposed lateral trough portions, and those flows produce damaging turbulence phenomena in the central trough. Those turbulence effects are further increased by the squish flow.
U.S. Pat. No. 5,390,634 describes a combustion chamber which is disposed in the cylinder head and in the piston crown. The piston crown has an irregular portion thereon which is intended to guide the mixture and produce turbulence therein. The squish surface portions promote the eddy formation effect, like also the asymmetrical combustion chamber in the piston crown.
German patent specification No. 35 11 837 discloses a further combustion chamber in which the piston has a step configuration for which there is a corresponding cooperating contour in the cylinder chamber. The surfaces in the form of a circular ring, which are afforded by the step configuration of the piston and the cylinder chamber, serve as surfaces for defining a fresh air chamber which is provided as a buffer. An annular gap which is formed between the peripheral wall of the piston in the region of the step configuration and the corresponding inside wall of the cylinder during compression and which forms a communication from the fresh air chamber to the combustion chamber is provided as a throttle means. Therefore, the fresh gases to be compressed are retarded when they pass from the fresh air chamber into the combustion chamber.
German laid-open application (DE-OS) No. 31 07 836 discloses a piston with an annular trough 12 for collecting the fresh gases and for producing a rotational movement of those gases about the axis of the annular configuration. In this case also there is no acceleration of the fresh gases.
Patent specification No. 91 636 of the German Democratic Republic discloses guiding the fresh gases in a predetermined direction through guide passages which are comparable to guide vanes of turbines.
The Abstract of Japanese patent application No. 07 019 051 shows how fresh gases are urged inwardly between a piston and a cylinder head and are passed by a guide element into the compression chamber which is disposed in the cylinder head.
Finally the Abstract of Japanese patent application No. 61-175225 discloses a combustion chamber whose center line is arranged in displaced relationship relative to the axis of the combustion chamber in the piston crown. In other words, combustion chamber portions are arranged in mutually displaced relationship. The displaced relationship and the squish gap cause turbulence phenomena to be produced in the fresh gases in the compression chamber. There is no mixture guide element. Furthermore, the fresh gases are not guided in a circular configuration.
The object of the present invention is to satisfy the conditions set forth in the opening part of this specification and to provide a combustion chamber which, while saving fuel, has a lower level of pollution emission in relation to the fuel consumption.
The foregoing object is attained by the features of Claim 1. Advantageous configurations are set forth inter alia in appendant Claims 2 and 3.
In the induction stroke, the fresh gases flow tangentially into the combustion chamber through one or more inlet valves. The fresh gas temperature is reduced at the cooled cylinder wall, due to the circulatory movement, whereby better filling is achieved and a higher level of compression is possible. This results in a higher power output with a reduction in specific fuel consumption.
In the compression stroke the circulatory movement of the fresh gases is maintained by a mixture guide element on the piston crown, in which respect a circular squish surface which serves here as an accumulation or deflector surface provides for the necessary upward movement. By virtue of the squish gap at top dead center, the fresh gases are urged in a circulatory mode inwardly, they collect at the center of the combustion chamber trough, and are fired by a spark electrode arranged on the longitudinal axis of the cylinder. Due to the central arrangement of the spark electrode, the flame front can spread rapidly and uniformly in all directions, which affords a reduction in the HC-proportion in the exhaust gas.
When burning diesel oil, an injection nozzle can be provided in place of the spark electrode on the longitudinal axis of the cylinder. As injection of the diesel oil takes place primarily into the combustion chamber trough in the piston crown, in which case the fuel is deposited in the form of a thin film on the wall surface of the trough, combustion is gentler and noise emission is lower.
In operation as a lean burn engine there are to be provided at least two inlet ducts each having a respective injection valve, in which case in the induction stroke a lean mixture flows into the cylinder and a rich mixture is excluded from bottom dead center to inlet. The injection valves are operated in succession. Upon compression, due to the way in which the fresh gas is guided and due to the squish gap, the rich mixture is concentrated in a circulatory manner in the combustion chamber trough of the piston crown, and fired.